With Knowledge comes Opportunity
With Opportunity comes Success

Technical Analysis Portal Financial Analysis Value Investing Behavioral Finance Portal
>Home Page >Behavioral Finance >Confirmation Bias:
Confirmation bias is the technical name for people's desire to find information that agrees with their existing view.
Confirmation bias refers to a type of selective thinking whereby one tends to notice and to look for what confirms one's beliefs, and to ignore, not look for, or undervalue the relevance of what contradicts one's beliefs. Numerous studies have demonstrated that people generally give an excessive amount of value to confirmatory information, that is, to positive or supportive data.
[Francis Bacon] "It is the peculiar and perpetual error of the human understanding to be more moved and excited by affirmatives than by negatives".
[Douglas Adams] "Human beings, who are almost unique in having the ability to learn from the experience of others, are also remarkable for their apparent disinclination to do so".
[Gilovich] "The most likely reason for the excessive influence of confirmatory information is that it is easier to deal with cognitively". It is much easier to see how a piece of data supports a position than it is to see how it might count against the position. The tendency to give more attention and weight to the positive and the confirmatory has been shown to influence memory. When digging into our memories for data relevant to a position, we are more likely to recall data that confirms the position.
[Heuer] "Information that is consistent with our existing mindset is perceived and processed easily. However, since our mind strives instinctively for consistency, information that is inconsistent with our existing mental image tends to be overlooked, perceived in a distorted manner, or rationalized to fit existing assumptions and beliefs. Thus, new information tends to be perceived and interpreted in a way that reinforces existing beliefs. The objective is to identify the most fundamental analytical assumptions, then to make these assumptions explicit so that they may be critiqued and re-evaluated. AND THIS IS KEY: "...The analyst should then try to disprove, rather than prove, each of the alternatives. He or she should try to rebut rather than confirm hypotheses...It is especially important for the analyst to seek information that, if found, would disprove rather than bolster his own arguments. One key to identifying the kinds of information that are potentially most valuable is for the analyst to ask himself what it is that could make him change his mind. Adoption of this simple tactic would do much to avoid intelligence surprises".
Publication Prejudices: An Experimental Study of Confirmatory Bias in the Peer Review System, MAHONEY
"Confirmatory bias is the tendency to emphasize and believe experiences that support one's views and to ignore or discredit those that do not. The effects of this tendency have been repeatedly documented in clinical research".
I'll See It When I Believe It - A Simple Model of Cognitive Consistency, Yariv, 2002
"Consider someone who buys an expensive car and later discovers that it is uncomfortable on long drives. Disagreement, or dissonance, exists between their beliefs that they have bought a good car and that a good car should be comfortable. Dissonance could be reduced by deciding this discomfort does not matter since the car is mainly used for short trips (decreasing the importance of the dissonant evidence) or focusing on the car's strengths such as safety, appearance, and handling (thereby adding more consonant evidence). The dissonance could also be eliminated by getting rid of the car, but this behavior is a lot harder than changing beliefs. Moreover, if ambiguous information about the car arrives (a friend comments "this looks like a really interesting car"), it is more likely to be interpreted as supporting the belief that the car is good ("the friend means the car looks really cool and unique") rather than countering it ("what is an interesting looking car? The friend must mean it looks like a real lemon. Maybe the fact it's uncomfortable on long drives shows."). This example illustrates two cognitive biases that are consistently observed in agents making decisions under uncertainty: cognitive dissonance and confirmatory bias. Cognitive dissonance states that after having taken an action people tend to change their beliefs about the relative agreeableness of this action. Confirmatory bias refers to the phenomenon of people interpreting new evidence in ways that confirm their current beliefs. The abundant psychological literature on these two biases (overviewed in Section II) indicates that people behave as if they have a taste for: 1. consistency between the action taken and the belief held at each point in the decision process and 2. consistency between beliefs in di¤erent stages of the decision process".
On Confirmation Bias and Deviations From Bayesian Updating, Chetan , 2003
"Confirmation Bias, predicts that individuals will exhibit systematic errors in updating despite the existence of learning opportunities. This paper formulates an experimental design to evaluate this behavioral heuristic within a non-strategic environment that motivates subjects financially. Subjects report probability estimates of the state of the world at the draw of each signal which may be conservative relative to a Bayesian. Indeed, pilot data indicate that both conservatism and confirmation bias are present in updating behavior".
Pitfalls to Avoid, RAPPAPORT and MAUBOUSSIN, 2001
"Investors tend to seek out information that supports their existing point of view while avoiding information that contradicts their opinion. This trap not only affects where investors go for information but also how they interpret the information they receive - too much weight is given to confirming evidence and not enough to disconfirming evidence. Investors often fall into the confirmation trap after making an investment decision. For example, once investors purchase a stock, they seek evidence that confirms their thesis and dismiss or discount information that disconfirms it. This leads to a loss of objectivity. We have found one technique particularly useful for managing the confirmation trap in the expectations investing process. Ask questions and conduct analysis that challenges your most cherished and firmly held beliefs about the company and industry. Posing disconfirming questions opens your mind to alternatives you haven't fully considered, improving your decision-making and, ultimately, your investment track record".